1. Field of the Invention
The present invention relates to a method for producing a damper pulley, and, more particularly, to a method by which a rubber body composing a dynamic damper is easily and firmly fixed, thereby improving the durability thereof.
2. Description of Related Art
A damper pulley generally has a pulley of a circular configuration, a ring-shaped damper-mass member located along an outer periphery of the pulley, and a rubber body press-fitted between the pulley and the damper-mass member. The rubber body and damper-mass member act as a dynamic damper which restrains torsional resonance vibrations of a rotary shaft.
One example of a conventional damper pulley is shown in FIG. 1. As shown, a pulley 10 has a cylindrical boss portion 12 at an axial center thereof, an annular main portion 14 extending radially outwardly from the cylindrical boss portion 12, and a flange portion 16 formed along an outer periphery of the annular main portion 14. The pulley 10 is integrally formed by casting. Outside the pulley 10, a ring-shaped damper-mass member 18 is located. A rubber body 20 of a uniform thickness is bonded to the inner surface of the damper-mass member 18. A cylindrical retainer plate 22 is bonded to the inner surface of the rubber body 20.
The retainer plate 22 is radially enlarged and press-fitted onto the outer surface of the flange portion 16. Due to the radial enlargement of the retainer plate 22, the rubber body 20 is compressed outwardly, whereby shrinkage strain within the rubber body 20 generated upon formation thereof can be eliminated.
The above-described conventional damper pulley is, however, of a significant weight because the pulley 10 formed of cast metal is thick. Thus, the production costs of casting are expensive.
Japanese Utility Model application laid-open No. Hei 3-114652 discloses a damper pulley which is provided to overcome the above-described problems. This damper pulley is produced by bending a metallic plate to provide an annular main portion and a flange portion at an outer periphery of the main portion, bonding a rubber body to both the flange portion and a ring-shaped damper-mass member by vulcanization, and enlarging the diameter of the flange portion radially outwardly to compress the rubber body, thereby eliminating the shrinkage strain within the rubber body.
With this method, the weight of the damper pulley and the production costs are both reduced and the production thereof is facilitated easily. However, these damper pulleys are still not satisfactory. In order to overcome the above-described problems, it is preferable to form the cylindrical boss portion integrally with the annular main portion and the flange portion. However, in the case where the boss portion is formed by deep drawing, the thickness of the main portion and the flange portion integral with the boss portion becomes small. As a result, in such a case, it becomes difficult to enlarge the diameter of the thin flange portion outwardly, and sufficient strength for the pulley cannot be obtained upon enlarging the flange portion.
Furthermore, an open end of the flange can deform with ease, however, a base end thereof, which is connected to the main portion, cannot be easily enlarged outwardly. This causes the rubber body not to be compressed uniformly, and there are cases where the rubber body undesirably falls-off due to the residual shrinkage strain therewithin.